A Community Antenna Television (CATV) system, often referred to simply as cable TV, typically is based on a branching tree network topology as representatively shown in FIG. 1. In accordance with this topology, the CATV system has a head end which receives signals from source programming and transmits these signals over the network. A trunk system forms a main artery for carrying the programming signals to subscribers.
This branching tree topology, in principle, is adaptable to expand interactive communications capabilities that are now available for communications highway network systems. One such system is described in U.S. Pat. No. 5,471,474 titled "Communications Highway Network System." This interactive system uses the distribution system of a CATV system infrastructure and a large number of system nodes that connect to the distribution system to establish a network.
Each system node of the network system described in U.S. Pat. No. 5,471,474 includes a CPU module for controlling the system node, an RF modem module for interfacing the system node to the distribution system, and a power supply. In this system, one of the system nodes acts as a system pacer/allocator which provides, among other things, global sychronization for all system nodes, and controls access to the network bus. The network system also uses channels of the CATV system for its transmissions between system nodes. These channels are considered the network bus. The network bus, which is used for communications between system nodes, has a forward channel and a reverse channel for two-way transmissions of information.
There long has been a desire to have equalization on the forward and reverse channels so that high quality signals are received by the system nodes. High quality signal transmission over the network provides a basis for expanded uses of the data transmitted on the network.
Transmissions over the network between the transmitter of one system node and the receiver of another system node experience path impairments, such as amplitude tilt, group delay error, signal reflections, and path loss. These impairments are different for transmissions between any specific transmitter-receiver pair because each transmitter-receiver pair is connected to the head end by a unique path. One way to compensate for these impairments is with packet-to-packet adaptive equalization, in which a node uses a preamble in each received packet to make adjustments. Such a process, however, is susceptible to problems due to noise and collisions on the network. Another problem is that an equalization training pattern must be available in each packet, thus increasing overhead. To overcome this, significant hardware additions are needed.